Investigations of Cosmic Ray Intensity Variations in Antarctica
Days of high planetary geomagnetic index (A 1,) for the period May through December 1966. From Solar-Geophysical Data (1967). Day of Yearl Date
I
A
146 May 26 78 151 May 31 48 190 July 9 36 242 Aug 30 82 246 Sept 3 92 247 Sept 4 112 251 Sept 8 42 278 Oct 5 36 304 Oct 31 34 348 Dec 14 48
ionosphere. In the antarctic region, the consequent temperature increase is sufficient to shift the scale height of the ionosphere upward to such an extent that the total electron content below the 1,000-km altitude of the satellites involved in this study is reduced. References
Mott, D. L. 1966. Geodetic satellite observations at McMurdo station. Antarctic Journal of the United States, 1(5): 187-188. Stephens, C. P. 1967. The antarctic ionosphere and its relation to geomagnetic activity during 1966. Masters thesis,
New Mexico State University, May 1967. da Rosa, A. V. and F. L. Smith III. 1967. Behavior of the nighttime ionosphere. Journal of Geophysical Research,
72(7): 1829-1836.
Solar-Geophysical Data. 1967. U.S. Department of Com-
merce, Environmental Science Services Administration, Boulder, Colorado. Report IER-FB-270, February 1967, p. 43.
Investigations of Cosmic Ray Intensity Variations in Antarctica MARTIN A. POMERANTZ Bartol Research Foundation of The Franklin Institute As a consequence of the role played by the geomagnetic field in determining the "optics" of cosmic ray detectors, it is possible to view directions of arrival of particles significantly inclined to the ecliptic plane only in the polar regions. Thus, observations made with continuously recording ground-based neutron monitors at fixed locations in the Arctic and Antarctic afford a unique means for investigating anisotropies that may arise in a direction perpendicular to the equatorial plane. A systematic cosmic ray intensity gradient along the Earth's rotational axis has been observed for the 170
first time. An analysis of data recorded by the network of high-counting-rate neutron monitors during the recovery phase of a Forbush decrease in March 1966 revealed the occurrence of a significant north-south asymmetry. Data from South Pole and McMurdo Stations were crucial in the discovery of this phenomenon. A theoretical model that accounts for all of the observed effects, including latitude dependence, has been developed. The anisotropy is envisaged as arising from the diffusion of cosmic rays through disordered magnetic fields in the vicinity of the Earth, the diffusion being associated with many conspicuous solar disturbances during this period of resurgent solar activity. The two components of the vector in three-dimensional space that defines the direction of anisotropy were determined by combining the information deduced from the study of the north-south asymmetry with data on the associated diurnal variation. During one of the two epochs that has been studied in detail, the greatest flux of cosmic ray particles was incident from the direction in space of -83.5 0 ± 3.50 declination and 13.3 ± 0.7 h right ascension. Thus, the configuration of the magnetic fields of solar origin that enveloped the Earth at this time was not symmetrical about the equatorial plane. Alternative interpretations of this result are (1) that the lines of force were temporarily directed almost perpendicularly to the solar equatorial plane, permitting the preferential flow of particles along these lines, or (2) that the lines of force were parallel to the equatorial plane, as usual, and the density gradient in the north-south direction was a consequence of the asymmetrical spatial distribution of the cosmic ray "shield." During 10 years of operation of neutron monitors in the polar regions, solar particles having sufficient energy to propagate to sea level (rigidity 1 GV) have been detected on only eight occasions. After a lapse of five years, the first flare-associated solarparticle emission that produced detectable effects in ground-based cosmic ray detectors occurred on July 7, 1966, following the 213 flare that commenced at 0020 UT. This event is especially noteworthy because it was the first observed by the network of high-counting-rate neutron monitors currently operating in both polar regions. The maximum increase was about two percent. The first significant effect occurred at 0115 UT, 55 minutes after the onset of the flare. A second and quite unusual event occurred on January 28, 1967. An analysis based upon a comparison of the recordings from South Pole (atmospheric depth, 694 g/cm 2 ) and McMurdo (atmospheric depth, 993 g/cm2 ) made it possible to determine the absorption coefficient of the solar cosANTARCTIC JOURNAL
35
this dumping. Plateau Station is so situated that signals from VLF transmitters that are recorded there pass either through, near, or far away from the magnetic anomaly, providing both observational and control data for this study.
30
25
Z 0 i- 20 >
W
15
Iz 10
La 11
b I Q 12 14 16 18 20 22 Hours, U.T
Percent deviation of absorption from normal level as recorded at four stations during the event of January 28, 1967.
mic rays. This event is anomalous in that either it represents the first observation of solar particles reaching the Earth from the back side of the sun or it is associated with a relatively feeble flare (
I
A
146 May 26 78 151 May 31 48 190 July 9 36 242 Aug 30 82 246 Sept 3 92 247 Sept 4 112 251 Sept 8 42 278 Oct 5 36 304 Oct 31 34 348 Dec 14 48
ionosphere. In the antarctic region, the consequent temperature increase is sufficient to shift the scale height of the ionosphere upward to such an extent that the total electron content below the 1,000-km altitude of the satellites involved in this study is reduced. References
Mott, D. L. 1966. Geodetic satellite observations at McMurdo station. Antarctic Journal of the United States, 1(5): 187-188. Stephens, C. P. 1967. The antarctic ionosphere and its relation to geomagnetic activity during 1966. Masters thesis,
New Mexico State University, May 1967. da Rosa, A. V. and F. L. Smith III. 1967. Behavior of the nighttime ionosphere. Journal of Geophysical Research,
72(7): 1829-1836.
Solar-Geophysical Data. 1967. U.S. Department of Com-
merce, Environmental Science Services Administration, Boulder, Colorado. Report IER-FB-270, February 1967, p. 43.
Investigations of Cosmic Ray Intensity Variations in Antarctica MARTIN A. POMERANTZ Bartol Research Foundation of The Franklin Institute As a consequence of the role played by the geomagnetic field in determining the "optics" of cosmic ray detectors, it is possible to view directions of arrival of particles significantly inclined to the ecliptic plane only in the polar regions. Thus, observations made with continuously recording ground-based neutron monitors at fixed locations in the Arctic and Antarctic afford a unique means for investigating anisotropies that may arise in a direction perpendicular to the equatorial plane. A systematic cosmic ray intensity gradient along the Earth's rotational axis has been observed for the 170
first time. An analysis of data recorded by the network of high-counting-rate neutron monitors during the recovery phase of a Forbush decrease in March 1966 revealed the occurrence of a significant north-south asymmetry. Data from South Pole and McMurdo Stations were crucial in the discovery of this phenomenon. A theoretical model that accounts for all of the observed effects, including latitude dependence, has been developed. The anisotropy is envisaged as arising from the diffusion of cosmic rays through disordered magnetic fields in the vicinity of the Earth, the diffusion being associated with many conspicuous solar disturbances during this period of resurgent solar activity. The two components of the vector in three-dimensional space that defines the direction of anisotropy were determined by combining the information deduced from the study of the north-south asymmetry with data on the associated diurnal variation. During one of the two epochs that has been studied in detail, the greatest flux of cosmic ray particles was incident from the direction in space of -83.5 0 ± 3.50 declination and 13.3 ± 0.7 h right ascension. Thus, the configuration of the magnetic fields of solar origin that enveloped the Earth at this time was not symmetrical about the equatorial plane. Alternative interpretations of this result are (1) that the lines of force were temporarily directed almost perpendicularly to the solar equatorial plane, permitting the preferential flow of particles along these lines, or (2) that the lines of force were parallel to the equatorial plane, as usual, and the density gradient in the north-south direction was a consequence of the asymmetrical spatial distribution of the cosmic ray "shield." During 10 years of operation of neutron monitors in the polar regions, solar particles having sufficient energy to propagate to sea level (rigidity 1 GV) have been detected on only eight occasions. After a lapse of five years, the first flare-associated solarparticle emission that produced detectable effects in ground-based cosmic ray detectors occurred on July 7, 1966, following the 213 flare that commenced at 0020 UT. This event is especially noteworthy because it was the first observed by the network of high-counting-rate neutron monitors currently operating in both polar regions. The maximum increase was about two percent. The first significant effect occurred at 0115 UT, 55 minutes after the onset of the flare. A second and quite unusual event occurred on January 28, 1967. An analysis based upon a comparison of the recordings from South Pole (atmospheric depth, 694 g/cm 2 ) and McMurdo (atmospheric depth, 993 g/cm2 ) made it possible to determine the absorption coefficient of the solar cosANTARCTIC JOURNAL
35
this dumping. Plateau Station is so situated that signals from VLF transmitters that are recorded there pass either through, near, or far away from the magnetic anomaly, providing both observational and control data for this study.
30
25
Z 0 i- 20 >
W
15
Iz 10
La 11
b I Q 12 14 16 18 20 22 Hours, U.T
Percent deviation of absorption from normal level as recorded at four stations during the event of January 28, 1967.
mic rays. This event is anomalous in that either it represents the first observation of solar particles reaching the Earth from the back side of the sun or it is associated with a relatively feeble flare (
